This invention relates to alumina-containing calcium silicate and a process for producing the same, and more particularly to secondary particles of alumina-containing calcium silicate, shaped bodies of such secondary particles of alumina-containing calcium silicate, aqueous slurries of such secondary particles of alumina-containing calcium silicate and processes for producing these secondary particles, shaped bodies and slurries.
Calcium silicate has found wide use in industries for refractory heat-insulating materials, fillers, adsorbents, reinforcing materials, building materials, etc. Since calcium silicate shaped bodies have the features of having high specific strength and heat-insulating properties and being light, highly dielectric and resistant to fire, they are expected to have wider application as inorganic materials. These characteristic properties appear attributable primarily to the form of calcium silicate crystals and to the structure of secondary particles of calcium silicate crystals in which the crystals are agglomerates and interconnected in a reticular arrangement.
We conducted research on the production and structure of secondary particles into which calcium silicate crystals are agglomerated in a peculiar mode and provided secondary particles of needlelike crystals of wollastonite group calcium silicate in the form of a porous shell which is globular to withstand external pressure most effectively with high stability and strength and which has a hollow interior and an outermost layer composed of closely interlocked crystals. We found that the secondary particles have high strength afforded by the globular shell-like form thereof and by the outermost layer of closely interlocked crystals and further possess an exceedingly low density because of their high degree of hollowness. We also found that shaped bodies with a very low density and high strength can be prepared from an aqueous slurry of such secondary particles merely by shaping the slurry and drying the shaped mass. Based on these findings, we accomplished an invention, which has matured to U.S. Pat. No. 4,162,924.
While the secondary particles described above have the distinct features that they are shaped to most effectively withstand external pressure with high stability and high strength and have a remarkably low apparent density, we have carried out continued research on various crystals in an attempt to replace the calcium silicate crystals constituting the secondary particles by other crystals without impairing these features in any way, and unexpectedly found that alumina-containing calcium silicate crystals are useful for realizing this entirely novel attempt and afford shaped bodies having further improved properties.